On the plane home from Japan, I saw Iron Man and The Dark Knight back to back, which was interesting. Obviously The Dark Knight is a far stronger film, being a serious Oscar contender and all that, but nonetheless it's striking for me how well Iron Man stands up to the comparison. It's not trying to be that kind of film, but instead is simply fun. I enjoyed it. It's certainly not crushed like an eggshell under Batman's tank, despite adhering almost slavishly to the superhero template that I'm coming to notice more and more.

What struck me particularly is how little these superhero films tend to differ from each other, especially the first in a series. You'll have the Superhero, the Villain and the Girl. The hero will have to go through about an hour's worth of character development before he experiences his Campbellian rebirth and dons the mask, unless we're dealing with an ensemble cast like the X-Men or the Fantastic Four. There will be lesser, rival Villains, but you'll never confuse them with the big banana. He's being played by an older big name actor. Finally there's the Girl, who for no intrinsic reason is always, always there. She'll be male if the hero is female (Catwoman, Elektra), but that's just a detail. Sometimes she's a baddie, but if so she'll be even more clearly sexualised to bring out the romantic tension. You'll even find her in all the Batman films, although only so far.

This triangle is getting familiar. I won't call it superhero-by-numbers, but only because I happen to like the genre. Bana, Connolly and Nolte. Neeson, Bale and Holmes. Maguire, Dunst and Defoe. Other characters will be sprinkled around the edges, but fundamentally they're all basically the same film. It's possible to ring the changes on this formula, but no one here was interested in that. Here we have Jeff Bridges, Gwyneth Paltrow, Robert Downey Jr and absolutely no surprises. This thing is almost exactly what you think it's going to be. It's loud, cool and utterly unconcerned to be sitting so cosily inside the box, so forget any hopes you might have had of thinking outside it. There's nothing you weren't expecting if you've so much as glimpsed the cover of an Iron Man comic in your life, but it's funny, confident and a recommendable waste of a couple of hours.

Firstly, Robert Downey Jr is terrific. It's his show, from start to finish, and he runs away with it like crazy. He's playing an irresponsible, hard-drinking, woman-chasing weapons manufacturer with every imaginable privilege and more money than Bruce Wayne. We should have been looking at the world's biggest prick, but Downey turns in what's probably the best superhero performance in a movie to date by having way too much fun and improvising all over the shop while never losing sight of Tony Stark's humanity and layers. Obviously he himself has had a colourful past. Drink-driving, prison sentences, multiple weapons charges, being thrown into secure drug rehabilitation centres... this is a man who knows about overindulgence. However I shouldn't be talking about that. The important thing is that Downey is funny and kicks arse.

Oh, and before anyone suggests it, Wolverine's a much easier role. That's not to say that Hugh Jackman doesn't put everything into it, of course.

Then there's Gwyneth Paltrow. I adore Gwyneth, even if I'm not wild about the red hair they've given her here. She has good chemistry with Downey and makes the most of a fairly one-dimensional part, even getting laughs out of her DIY heart surgery. "There's pus! It smells!"

The third of the triad is Jeff Bridges, who's having as much fun as everyone else on the set. I was spooked by his beard, though. It's like a cliff face. The laws of superhero films dictate that he will be the villain and so it proves, with the film not really putting any effort into either convincing us otherwise or, oddly, giving him much to do. The plot's less important than just letting the actors roll out their characters, so the fact that on paper this is a fairly underwritten role doesn't stop Bridges from being a lot of fun in it.

That's what's important. What I admire is the way it has the confidence to put so much weight on the character work of its three main actors, to an extent that relegates the plot to second place. There are fun details, such as the likeable, sometimes rather sweet soldiers and the way in which Tony Stark's destructive suit testing is much more fun than Batman's similar equipping in Batman Begins. Terrence Howard has managed to get himself thrown off the series as Rhodey, but I can't say I'll miss him in the sequel. He's okay. The world's full of actors who're okay. Let's see how his replacement fares. Oh, and you might spot Foggy Nelson from Daredevil (2003) as one of Stark's employees. That's the director, Jon Favreau, in what's basically a glorified cameo.

They're aiming for something resembling a realistic tone, so Stark gets captured by terrorists in Afghanistan. This makes them appropriately scummy and evil, but not really a match for Iron Man. Well, he's cool and they have some really big weapons, so that's okay. Note that I didn't actually call this thing realistic, so I can forgive the way in which falling out of the sky isn't fatal if you're wearing a metal suit.

The key word for this movie is "fun". I've written that word so much in this review that I ended up getting self-conscious and rephrasing my sentences to avoid it. It's a character-based film, but it's never in danger of disappearing up its own arse after the fashion of one or two films based on DC heroes. Robert Downey Jr gives us a charming, wildly flawed hero with a refreshing lack of concern for restraint and reasonable force. Don't go in expecting surprises or anything too closely resembling a plot and you'll be fine.